1. Field of the Invention
The present invention relates to a process for producing granules of polycarbonate or a polycarbonate composition, and more particularly, to a process for the production thereof from a solution of polycarbonate or a polycarbonate composition.
2. Description of the Related Art
There have been proposed various methods for isolating polycarbonate from solution of polycarbonate.
For example, Japanese Patent Publication No. Sho 38-22497 discloses that a solution of polycarbonate in an organic solution is concentrated, crystallized and then ground. This method requires a long time for forming a crystallized state which can be ground and therefore, it is not industrially efficient.
There are known methods for precipitating polycarbonate by adding methanol (Japanese Patent Publication No. Sho 36-22447) or acetone, ethyl acetate and the like (Japanese Patent Publication No. Sho 37-7000) to a solution of polycarbonate in an organic solvent. The polycarbonate produced by the methods are of a low bulk density in the form of fine powder. There is also proposed a method for producing polycarbonate by heating a solution of polycarbonate in an organic solvent in a water medium to evaporate and remove the organic solvent (U.S. Pat. No. 3,505,273). This method gives, in general, sticky lumps so that stirring should be sufficiently effected.
Many improved methods for preventing the formation of lumps in a water medium are proposed.
For example, U.S. Pat. No. 4,423,207 discloses a method for spraying a solution of polycarbonate in an organic solvent into a warm water;
Japanese Patent Laid-open No. Sho 60-116412 discloses a method where a solution of polycarbonate in dichloromethane is fed to a particle making vessel and dichloromethane is evaporated at 1.1-50 atmospheric pressure while the suspension stated is kept in water;
Japanese Patent Laid-open No. Sho 59-133228 discloses a method comprising forming polycarbonate particles by feeding continuously a solution of polycarbonate in dichloromethane to a warm water in a particle making vessel to form polycarbonate particles, wet-grinding at least a part of the water slurry containing the polycarbonate particles, and then recirculating the product thus wet-ground to the particle making vessel;
Japanese Patent Laid-open No. Sho 60-202126 discloses a method comprising feeding a solution of polycarbonate in dichloromethane to a kneader having a grinding mechanism and reserving a hot water kept at a temperature of the boiling point of dichloromethane or higher, and kneading the polycarbonate to effect simultaneously removing the solvent and grinding;
Japanese Patent Laid-open No. Hei 1-74231 discloses a method for producing polycarbonate particles which comprises placing polycarbonate particles in a warm water, providing a narrow flow channel in the stirring flow of the warm water, applying a shearing force by rotating a stirring vane at a high speed in this flow channel to cause a high speed convection of the warm water, and feeding a solution of polycarbonate in dichloromethane to the warm water; and there are other methods.
However, any of them requires high pressure conditions, special apparatuses such as wet type grinders, kneaders and the like, and/or special conditions. Therefore, a simpler method for isolating polycarbonate from solution of polycarbonate has been demanded.
On the other hand, U.S. Pat. No. 4,668,768 discloses a method for producing polycarbonate powder which comprises adding an anti-solvent for polycarbonate such as methyl ethyl ketone, methyl isobutyl ketone and the like and water to a solution of polycarbonate in an organic solvent and then heating to evaporate and remove the organic solvent. The resulting polycarbonate powder contain, however, fine powder of polycarbonate so that flying of the fine powder occurs upon storing, bagging and molding, and further, bridging occurs in hoppers of extruding molding machine. Therefore, there are problems in handling such as flying and flowing property of the powder.
Further, as a method for producing polycarbonate having a large particle size, the following methods are known.
For example, Japanese Patent Publication No. Sho 46-31468 discloses a method for producing porous polycarbonate granules which comprises adding a lower alkyl-substituted benzene as a swelling agent for polycarbonate to a solution of polycarbonate in an organic solvent, evaporating and removing most of the organic solvent to form the gel, making the gel into granules and evaporating the organic solvent and the swelling agent;
Japanese Patent Laid-open No. Sho 61-250026 discloses a method for solidifying polycarbonate by circulating a liquid for solidifying in a wet-grinding machine in a process for adding a solvent for solidification to a solution of polycarbonate in an organic solvent followed by mixing, distilling off the organic solvent and the solvent for solidification to produce a water slurry of polycarbonate; and
U.S. Pat. No. 4,603,194 discloses a method for producing polycarbonate granules which comprises adding a solution of polycarbonate in an organic solvent to water containing suspended polycarbonate particles and evaporating and removing the organic solvent.
According to the method of producing porous polycarbonate particles of Japanese Patent Publication No. Sho 46-31468, rice cake-like matters are formed in the process of solidification and said matters should be ground by stirring and therefore, much power is required and the stirring becomes often difficult.
According to the method of Japanese Patent Laid-open No. Sho 61-250026, a special particle making vessel is required which is equipped with a wet type grinding machine, and since a solvent for solidification is added to a solution of polycarbonate in an organic solvent to be fed, precipitation of polycarbonate occurs during the feeding and thereby sometimes the solution of polycarbonate in an organic solvent can not be smoothly fed.
In addition, according to the method of U.S. Pat. No. 4,603,194, polycarbonate granules substantially free from fine powder thereof can be obtained, but for purposes of obtaining polycarbonate granules having uniform particle size, the amount of polycarbonate particles, velocity of feeding the solution of polycarbonate in an organic solvent and the speed of distilling off the organic solvent should be strictly controlled, and lumps are often formed.